This invention relates generally to a dishwasher having a selectively controllable wash liquid recirculation system and more specifically to a dishwasher having a rotatable flow director or diffuser for directing the flow of wash liquid recirculated within the dishwasher.
Generally, a dishwashing machine has a wash cavity supporting an upper and lower wash rack wherein a horizontally rotatable lower spray arm is disposed beneath the lower rack and an upper spray arm is disposed below the upper rack. Alternative to the upper spray arm, a center, telescopically mounted tube extending upwardly from the lower spray arm may be provided. A wash pump recirculates wash liquid throughout the wash chamber by drawing wash liquid from the wash cavity sump and supplying wash liquid to the upper and lower spray arms such that the spray arms direct wash liquid spray through nozzles to the dishes supported by the upper and lower racks, respectively.
Prior art dishwashers have several limitations or problems to which the present invention is directed.
One limitation is that dishwashers typically have spray arms which rotate under the reactive force of the liquid discharged from the arm. This requires that at least one, and typically two, spray arm nozzles must be configured to provide the required reactive force to ensure proper spray arm rotation rather than being configured to provide the optimum spray pattern for optimum washing results. Moreover, as a result of the fixed nozzle design, the spray arms always rotate in the same direction when the pump supplies wash liquid to the spray arms. This results in a constant spray pattern onto dishes supported on the upper and lower racks.
Another common shortcoming in dishwasher designs is the problem of soil redeposition on the clean dishes during drain, which is most evident in a reversible pump system wherein a centrifugal soil separator is used in conjunction with a pump driven by a reversible pump. In a first motor direction, a wash impeller of the pump operates to supply wash liquid to the wash arms and pump wash liquid through a soil settling chamber such that soils are removed from the recirculating wash liquid. In a second motor direction, a drain impeller of the pump operates to pump wash liquid out of the wash cavity through a drain hose.
In this configuration, during drain mode operation, the wash impeller also is rotated, there being a single motor for driving both impellers. Although the wash impeller's effectiveness is greatly reduced in the reverse motor direction, the wash impeller still operates to pump a small amount of wash liquid through the wash arms during the drain mode. When the motor is reversed, causing the pump to transition from the wash mode to the drain mode, dynamic changes in the fluid flow through the sump of the wash cavity stir up soils. These soils are pumped, by the action of the wash impeller during the drain mode, through the wash arms where they may be redeposited onto dishes. As the wash liquid is pumped to drain, the wash impeller is eventually starved, preventing further pumping of wash liquid through the spray arms and leaving the soils on the dishes.
Yet another limitation in dishwasher design is the amount of hot water required to adequately operate the dishwasher pump system. Prior art dishwasher pump systems generally are configured to supply wash liquid simultaneously through both the upper and lower spray arms during the wash cycle. To adequately supply wash liquid to both of the spray arms simultaneously, a flow rate between 30-40 GPM is typical. As is readily understood by one skilled in the art, enough water must be provided to keep the pump primed while providing this flow rate.
Increasingly, the appliance industry is under pressure to reduce energy consumption. Since one of the primary factors in dishwasher energy usage is the amount of hot water used, it would be advantageous to reduce the flow rate requirements of the dishwasher such that less hot water may be used.
U.S. Pat. No. 4,509,687 discloses a system for alternatingly diverting the flow of wash liquid between a rotating spray arm and an extendable top spray tower. A gear system is provided wherein a driving gear drives a fixed reaction gear to control the rotation of a valve which directed liquid flow between the spray arm and the tower. This system is relatively complicated and results in an automatic and non-selectively controllable oscillation between suppling wash liquid to the spray arm and spray tower.
U.S. Pat. No. 4,094,702 discloses a dishwasher system having an upper and lower spray arm wherein a valve is provided which may be manually operated for allowing independent control of the washing liquid flow to the respective upper and lower spray arms. This system has the significant disadvantage of requiring the user to manually select the control of wash liquid flow.